1. Field of the Invention
The present invention relates to acoustic transducer units and, more specifically, to acoustic transducer units accommodating acoustic transducer elements, such as microphones or speakers, in housings.
2. Description of the Related Art
The present invention relates to acoustic transducer units and, more specifically, to acoustic transducer units accommodating acoustic transducer elements, such as microphones or speakers, in housings.
When an electromagnetic shield is formed around elements in a structure in which the elements are arranged on a substrate and are covered with a cap member, for example, a structure according to a comparative example shown in a sectional view in FIG. 16 may be adopted. That is, a microphone element 2 is mounted on a multilayer substrate 30x having conductive layers 30y for electromagnetic sealing therein and is bonded thereto with wires 3. Then, a cap member 20x having a conductive layer 20y for electromagnetic sealing, which is formed by plating or the like, is bonded to the multilayer substrate 30x so as to cover the microphone element 2. An acoustic path 80 communicating between the outside of the housing and the microphone element 2 is formed inside the multilayer substrate 30x. 
However, the structure of FIG. 16 has the following problems.
First, because the element is mounted face up, a wiring space is needed. Thus, it is impossible to reduce the size and height. Furthermore, because unnecessary volume is large, an acoustically optimum design is impossible.
Second, because the multilayer substrate and the cap member are made to have an electromagnetic shielding function, the structure of the multilayer substrate becomes complex and treatment for giving conductivity to the cap member, e.g., plating, is needed. These increase costs.
Third, because the acoustic path is formed in the multilayer substrate, the manufacturing method for the multilayer substrate is complex and difficult. This increases the cost of the substrate. Furthermore, seepage of adhesive into the acoustic path or deformation of the acoustic path occurring in the manufacturing process of the substrate causes variation in performance. This makes the manufacture troublesome and increases costs.